(Circulation. 1996;93:932-939.)
© 1996 American Heart Association, Inc.
Articles |
Alteration in Energetics in Patients With Left Ventricular Dysfunction After Myocardial Infarction
Increased Oxygen Cost of Contractility
Presented in part at the 65th Scientific Sessions of the American Heart Association, New Orleans, La, November 18, 1992, and previously published in abstract form (Circulation. 1992;86[suppl I]:I-647).
From the 1st Department of Internal Medicine, Kobe (Japan) University School of Medicine.
Correspondence to Motoshi Takeuchi, MD, PhD, The 1st Department of Medicine, Kobe University School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe, 650 Japan.
Background Although the use of inotropic agents to treat congestive heart failure (CHF) in patients with coronary artery disease has yielded short-term hemodynamic improvement, long-term mortality has shown less improvement. The loss of cardiac muscle as a result of infarction not only decreases the pumping ability of the heart but also leads to some dramatic changes in myocardial energetics. However, little is known about the mechanoenergetics of the heart in patients with left ventricular (LV) dysfunction after myocardial infarction.
Methods and Results The present study was designed to
compare, by means of the
O2-pressure-volume area
relation
(PVA, a measure of total mechanical energy) and Emax (LV
contractility index), the incremental oxygen cost of
contractility measured as nonmechanical energy per unit
increment in contractility in patients with various
kinds of LV dysfunction. We assessed Emax,
O2, and PVA using
conductance and
Webster catheters under control conditions and during different rates
of dobutamine infusion (3 and 6
µg·kg-1·min-1)
in 30 patients with coronary artery disease. Patients were
divided into three groups according to LV ejection fraction (EF): 10
without LV dysfunction (EF 
60%), 10 with mild LV dysfunction
(40%
EF<60%), and 10 with severe LV dysfunction (EF <40%). Under
control conditions, the
O2-PVA relation
was linear in each group. Contractile efficiency, the reciprocal of the
slope of this relation, was comparable among the three groups. The
oxygen cost of contractility in the severe LV
dysfunction group was significantly greater than in the groups without
and with mild LV dysfunction (0.022±0.014 versus 0.005±0.002 and
0.0012±0.005 mL O2 · mL · mm
Hg-1 per beat, P<.05).
Conclusions These findings suggest that the alteration in mechanoenergetics in patients with severe LV dysfunction after myocardial infarction may result from the increased oxygen cost of excitation-contraction coupling rather than from a reduction in the efficiency of chemomechanical energy transduction.
Key Words: ventricles • oxygen • contractility • heart failure
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